When Stardock released SOASE originally, they put no copy protection, and essentially allowed players to "obtain" the single player mode for free (Assuming you didn't want to buy the game legitimately)
Multiplayer mode required you pay them money.
I remember Stardock posting that if people wanted to pay for a quality product, they would. Otherwise they were happy with their game simply being played (Although I'm positive they are more happy with playing and paying customers!).
And that's still how it is now.
If it were released on steam, that statement would become void as Steam, generally, extensive copy protection on its products.
Not really. GCF extractors can easily extract many parts from Valve-Steam games (sounds images models etc), and third party games are often put on Steam in the same exact format their original developer presented it.
That is, if Sins were put onto Steam, it would probably be accessible just as it is now, but would be in a different location on your file system: that is,
C:\Program Files\Stardock Games\Sins of a Solar Empire - Trinity
would probably correspond exactly to
C:\Program Files\Steam\steamapps\common\Sins of a Solar Empire - Trinity
(if Sins was put on Steam)
It would very likely either be put there or here:
C:\Program Files\Steam\steamapps\STEAMUSERNAME\Sins of a Solar Empire - Trinity
and from that location everything accessible from the Stardock file path would be accessible from one of the above paths. No copy protection. Especially not for third-party games.